There are numerous existing methods and apparatus for mechanically coupling or joining bars in the building industry. One important problem encountered is the joining of reinforcing bars used in reinforced concrete structures. While welding the bars together may appear to be the most effective method, the process of welding affects the martensitic structure of the individual bars resulting in an under-strength joint.
One prior art method relies on threading the ends of reinforcing bars to be joined, so that they can be screwed into an intermediate coupler in which female threads have been cut. This method, however, has the disadvantage of strength, having to directly thread the bar itself, thereby removing an outer layer of the reinforcing bar with the consequential reduction of the strength of the coupled joint.
A further method used in the prior art to join reinforcing bars requires that an outer tube be placed over the ends of the bars to be joined and fractable studs to be screwed in to engage the bars. This method is costly and relies on on-site work skills in ensuring that the coupler is installed correctly.
A further method requires one of the bars to be contained within an outer tubing wherein the outer tubing is filled with a non shrink grout. This method requires a very large outer tube which often cannot conform to concreting cover requirements and requires a high level of skill to be correctly installed.
Yet a further method involves the ends of reinforcing bars to be forged so that the forged ends can be connected without the need of rotating the bars. This method requires a third part outer sleeve or other method of containing the joined bars during construction. One example of this latter method is where the forged ends resemble castellations or interlocking tongues and grooves which require a sleeve in order to maintain the co-axial integrity of the join. This method has the disadvantage of having to be tightly constrained by an outer tube or similar device during installation.
A further method of joining reinforcing bars requires the friction welding of matching male and female threaded ends to lengths of reinforcing bar. These matching ends can be joined by counter rotating the bars so that the friction welded joiner ends screw together. This method has the disadvantage of requiring long lengths of bar to be rotated by the number of turns needed to complete the screwing together of the joint.
In all of the above prior art methods of joining reinforcing bars, not only is there a reliance on the skill of the operator, but the actual diligence of the operator to effect a secure join. There have been instances of screwed joints which have only been screwed a few turns on the end of the bars because of laziness or carelessness on the part of the operator. This can have dire consequences, especially in high rise buildings which rely on the integrity of reinforced concrete structures several floors up.